(Nicholas Louis de la), an eminent mathematician and astronomer, was born at a small town in the diocese of Rheims in 1713. His father had served in the army, which he quitted, and in his retirement studied mathematics; and amused himself with mechanic exercises, wherein he proved the happy author of several inventions of considerable use to the public. Nicholas, almost in his infancy, took a fancy to mechanics, which proved of signal service to him in his mature years. He was sent young to school at Mantes-sur-Seine, where he discovered early tokens of genius. In 1729, he went to Paris; where he studied the classics, philosophy, and mathematics. Afterwards he went to study divinity at the college de Navarre, proposing to embrace an ecclesiastical life. At the end of three years he was ordained a deacon, and officiated as such in the church of the college de Mazarin several years; but he never entered into priests orders, apprehending that his astronomical studies, to which he became most assiduously devoted, might too much interfere with his religious duties. In 1739, he was conjoined with M. de Thury, son to M. Caffini, in verifying the meridian of the royal observatory through the whole extent of the kingdom of France. In the month of November the same year, whilst he was engaged day and night in the operations which this grand undertaking required, and at a great distance from Paris, he was, without any solicitation, elected into the vacant mathematical chair which the celebrated M. Varignon had so worthily filled. Here he began to teach about the end of 1740; and an observatory was ordered to be erected for his use in the college, and furnished with a suitable apparatus of the best instruments. In May 1741, M. de la Caille was admitted into the royal academy of sciences as an adjoint member for astronomy. Besides the many excellent papers of his dispersed up and down in their memoirs, he published Elements of geometry, mechanics, optics, and astronomy. Moreover, he carefully computed all the eclipses of the sun and moon that had happened since the Christian era, which were printed in a book published by two Benedictines, entitled l'Art de verfer les dates, &c. Paris, 1750, in 4to. Besides these, he compiled a volume of astronomical ephemerides for the years 1745 to 1755; another for the years 1755 to 1765; a third for the years 1765 to 1775; an excellent work entitled Astronomia fundamenta novissimis folis et stellarum observationibus stabilita; and the most correct solar tables that ever appeared. Having gone through a seven years series of astronomical observations in his own observatory, he formed a project of going to observe the southern stars at the Cape. Cape of Good Hope. This was highly approved by the academy, and by the prime minister Comte de Argenson, and very readily agreed to by the states of Holland. Upon this, he drew up a plan of the method he proposed to pursue in his southern observations; setting forth, that, besides settling the places of the fixed stars, he proposed to determine the parallax of the moon, Mars, and Venus. But whereas this required correspondent observations to be made in the northern parts of the world, he sent to those of his correspondents who were expert in practical astronomy previous notice, in print, what observations he designed to make at such and such times for the said purpose. At length, on the 21st of November 1750, he sailed for the Cape, and arrived there on the 19th of April 1751. He forthwith got his instruments on shore; and, with the assistance of some Dutch artificers, set about building an astronomical observatory, in which his apparatus of instruments was properly disposed of as soon as it was in a fit condition to receive them.

The sky at the Cape is generally pure and serene, unless when a south-easter wind blows. But this is often the case; and when it is, it is attended with some strange and terrible effects. The stars look bigger, and seem to taper; the moon has an undulating tremor; and the planets have a sort of beard like comets. Two hundred and twenty-eight nights did our astronomer survey the face of the southern heavens; during which space, which is almost incredible, he observed more than 10,000 stars; and whereas the ancients filled the heavens with monsters and old-wives' tales, the abbe de la Caille chose rather to adorn them with the instruments and machines which modern philosophy has

* See the mode of use for the conquest of nature*. With no Planisphere less success did he attend to the parallax of the moon, in his Catalogue astrale Bellifèreum.

Having thus executed the purpose of his voyage, and no present opportunity offering for his return, he thought of employing the vacant time in another arduous attempt; no less than that of taking the measure of the earth, as he had already done that of the heavens. This indeed had, through the munificence of the French king, been done before by different sets of learned men both in Europe and America; some determining the quantity of a degree under the equator, and others under the arctic circle: but it had not as yet been decided whether in the southern parallels of latitude the same dimensions obtained as in the northern. His labours were rewarded with the satisfaction he wished for; having determined a distance of 410,814 feet from a place called Klip-Fontyn to the Cape, by means of a base of 38,802 feet, three times actually measured: whence he discovered a new secret of nature, namely, that the radii of the parallels in south latitude are not the same as those of the corresponding parallels in north latitude. About the 23rd degree of south latitude he found a degree on the meridian to contain 342,222 Paris feet. He returned to Paris the 27th of September 1754; having in his almost four years' absence expended no more than 9144 livres on himself and his companion; and at his coming into port, he refused a bribe of 100,000 livres, offered by one who thirsted less after glory than pain, to be sharer in his immunity from custom-house searches.

After receiving the congratulatory visits of his more intimate friends and the astronomers, he first of all thought fit to draw up a reply to some strictures which professor Euler had published relative to the meridian, and then he settled the results of the comparison of his own with the observations of other astronomers for the parallaxes. That of the sun he fixed at $9^\circ 56'$; of the moon, at $56' 56''$; of Mars in his opposition, $36'$; of Venus, $38'$. He also settled the laws whereby astronomical refractions are varied by the different density or rarity of the air, by heat or cold, and dryness or moisture. And, lastly, he showed an easy, and by common navigators practicable, method of finding the longitude at sea by means of the moon, which he illustrated by examples selected from his own observations during his voyages. His fame being now established upon so firm a basis, the most celebrated academies of Europe claimed him as their own; and he was unanimously elected a member of the royal society at London; of the institute of Bologna; of the imperial academy at Petersburg; and of the royal academies of Berlin, Stockholm, and Göttingen. In the year 1760, Mr de la Caille was attacked with a severe fit of the gout; which, however, did not interrupt the course of his studies; for he then planned out a new and immense work, no less than a history of astronomy through all ages, with a comparison of the ancient and modern observations, and the construction and use of the instruments employed in making them. In order to pursue the task he had imposed upon himself in a suitable retirement, he obtained a grant of apartments in the royal palace of Vincennes; and whilst his astronomical apparatus was erecting there, he began printing his Catalogue of the southern stars, and the third volume of his Ephemerides. The state of his health was, towards the end of the year 1763, greatly reduced. His blood grew inflamed; he had pains of the head, obstructions of the kidneys, loss of appetite, with an opulence of the whole habit. His mind remained unaffected, and he resolutely persisted in his studies as usual. In the month of March, medicines were administered to him, which rather aggravated than alleviated his symptoms; and he was now sensible, that the same distemper which in Africa, ten years before, yielded to a few simple remedies, did in his native country bid defiance to the best physicians. This induced him to settle his affairs: his manuscripts he committed to the care and discretion of his esteemed friend M. Maraldi. It was at last determined that a vein should be opened; but this brought on an obstinate lethargy, of which he died, aged 49.